In the bottling industry, reclosable containers are usually sealed with screw-type caps. To achieve a high productivity, the container sealing operation is performed by automatic capping machines processing in succession the containers transported in serial order on a conveyor belt or on any other type of materials handling machine. In typical capping machines, the container sealing operation is a two-step process. Firstly, the open container passes underneath a cap dispensing station applying loosely on the container neck a screw-type cap in thread alignment with the threads on the container neck (for the purpose of this specification, the term "thread alignment" designates a condition where the cap is not threadedly engaged on the container neck, however the threads on the cap and on the neck respectively are so disposed that rotation of the cap will cause the threads to mate in the correct fashion resulting in thread engagement. In contrast, "thread misalignment" will be used to identify a condition where rotation of the cap will cause improper thread engagement resulting in a poorly sealed container). The container is then transported to a cap tightening station where a chuck rotatably grips the cap, tightening same and sealing the container.
The accurate positioning of the cap on the container neck is a critical operation to ensure a proper thread engagement during the cap tightening stage. With currently available equipment, the method which is used to deposit the caps on the containers at the cap dispensing station is extremely simple. The caps are fed from a supply chamber or magazine to a cap dropping aperture where a latch drops the caps on the containers in a timed relationship with the container feed rate. Although a cap is dropped only a very short distance from the top of a container neck, during its free fall, the cap may slightly tilt, landing in an improper position on the container, failing to produce the desired thread alignment condition. Deep caps or caps with large threads, have inherent self-centering capability and accordingly, they can compensate, to a certain extent, for an imprecise positioning. However, shallow caps and caps with smaller thread sizes, have little ability to self-center themselves, in which case an improperly positioned cap will fail to produce a correct thread engagement during the cap tightening operation, resulting in a poorly sealed container.